pylama: Use %s instead of %t

Although using %t to lint changes was desirable, many pylama checks use
surrounding paths and file contents (e.g. C0103 module name, E0402
relative import beyond top, etc.)  The more such errors I find during
testing, the less %t seems like a good idea.  Switch to %s.

Also set `lint_file` to 1 and mark Pylama as a file linter in the docs.

Signed-off-by: Kevin Locke <kevin@kevinlocke.name>

test/command_callback/test_pylama_command_callback.vader

@@ -3,7 +3,7 @@ Before:
   call ale#test#SetFilename('test.py')
 
   let b:bin_dir = has('win32') ? 'Scripts' : 'bin'
-  let b:command_tail = ' %t'
+  let b:command_tail = ' %s'
 
 After:
   unlet! b:bin_dir